1. Field of the Invention
This invention relates to a tunable external cavity light source and a process for adjusting such a source.
2. Related Art
Continuously tunable light sources allow many uses, particularly in optical telecommunications, for example in multi-channel coherent communication systems, for spectroscopic measurements, and for laser and optical amplifier characterizations.
A continuously tunable light source has been described in French Patent No. FR-2 595 013, and more recently in an article by the inventors of the present application published in the review "Electronics Letters" of 17 Jan. 1991 (Vol. 27; No. 2. pp. 183-184).
The source described in these publications comprises a semiconductor laser with a first antireflection coated facet.
The second facet of this laser forms a resonant cavity with a diffraction grating.
The shifting of this grating, by combined rotation/translation, in predetermined conditions, allows to obtain the continuous tuning of the source.
These grating shifting conditions must be satisfied with great accuracy, and require the adjustment of mechanical components after the complete assembly of the source, regularly and even, preferably , frequently during its use.
Until now, the making of these adjustments was considered as particularly delicate, and no satisfactory method had been devised to permit the simple and routine use of such a source.